The disclosure of Japanese Patent Application Nos. 2000-94916 and 2000-253274 filed on Mar. 30, 2000 and Aug. 24, 2000, respectively, are incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to a fluid-filled vibration-damping device which has a fluid chamber or chambers filled with a non-compressible fluid. More particularly, the present invention is concerned with a pneumatically operated fluid-filled vibration-damping device which includes a fluid chamber partially defined by one of opposite surfaces of an elastic oscillating plate and an oscillating air chamber partially defined by the other surface of the elastic oscillating plate, and which is operable by applying a suitable air pressure change to the oscillating air chamber so that the vibration damping device exhibits desirably controlled damping characteristics thereof.
2. Description of the Related Art
As one type of a vibration damper such as a vibration damping bushing or a vibration damping mount, for flexibly connecting two members in a vibration system or mounting one of the two members on the other member in a vibration damping fashion, there is known a pneumatically operated fluid-filled vibration damping device, as disclosed in Japanese Laid-Open Publication No. JP-A-10-184770. Such a known pneumatically operated fluid-filled vibration damping device includes: a first and a second mounting members, which are spaced apart from each other; an elastic body elastically connecting the first and second mounting members and partially defining a primary fluid chamber filled with a non-compressible fluid; a flexible diaphragm partially defining an auxiliary fluid chamber filled with the non-compressible fluid and having a variable volume; a partition member fixed to the second mounting member such that the primary fluid chamber is disposed on one of opposite sides of the partition member and the auxiliary fluid chamber is disposed on the other side of the partition member; means for defining a first orifice passage for fluid communication between the primary and auxiliary fluid chambers; and an elastic oscillating plate partially defining on one of opposite sides thereof the pressure receiving chamber and on the other side thereof an oscillating air chamber, to which a suitably controlled periodic change of an air pressure is applied to the oscillating air chamber so that the elastic oscillating plate is oscillated by an oscillating force having a frequency corresponding to the frequency of the vibration to be damped. This type of the vibration-damping device is capable of controlling its vibration damping characteristics by adjusting the frequency or other factors of the periodic change of the air pressure applied to the oscillating air chamber. Therefore, this type of the vibration damping device has been suitably applied to vibration dampers such as an engine mount, which require to damp input vibrations whose frequencies and other factors are variable.
As is understood from the above-indicated publication, the known vibration damping device uses a disk-like shaped rubber elastic plate as the elastic oscillating plate which is oscillated to transmit the oscillating force caused by the periodic change of the air pressure in the oscillating air chamber to the primary fluid chamber to cause a pressure change of the fluid in the primary fluid chamber. The rubber elastic plate is fixedly supported at its peripheral portion by a member on the side of the second mounting member, and the first orifice member is disposed radially outwardly of the rubber plate for fluid communication between the primary and auxiliary fluid chambers.
In the known vibration damping device, the rubber elastic plate is desirably required to have a relatively large area so that the vibration damping device exhibits a high damping effect even in the case where the vibration to be damped has a relatively large vibrational energy.
However, the known vibration damping device constructed as described above needs to leave a space for disposing the first orifice passage at the radially outward portion of the rubber elastic plate, making it difficult to increase a diameter of the rubber elastic plate, resulting in difficulty in obtaining a sufficiently large area of the elastic rubber plate within a limited tolerable range of the outer diameter of the vibration damper.
Moreover, the rubber elastic plate whose diameter is increased to provide a sufficiently large area thereof is prone to be oscillated with a relatively large amplitude at its central portion. This may cause interference between the rubber elastic plate and other members incorporated within the vibration damper, resulting in deterioration of damping capacity of the device, generation of noises, and undesirable damages of the rubber elastic plate and the other members. In order to avoid the above-indicated interference between the rubber elastic plate and the other incorporated members, the vibration-damping device is inevitably made large in size.
It is therefore an object of this invention to provide a pneumatically operated fluid-filled vibration damping device which has a novel structure suitable for obtaining a sufficiently large area of an elastic oscillating plate while limiting the size of the device, and suitable for limiting an amount of maximum displacement of the elastic oscillating plate upon oscillation thereof.
The above and other objects of this invention may be attained according to the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principle of the invention is not limited to those modes of the invention and combinations of the technical features, but may otherwise be recognized based on the thought of the present invention that disclosed in the whole specification and drawings or that may be recognized by those skilled in the art in the light of the disclosure in the whole specification and drawings.
(1) A fluid-filled vibration damping device comprising: a first and a second mounting member which are spaced apart from each other; an elastic body elastically connecting the first and second mounting members and partially defining a primary fluid chamber filled with a non-compressible fluid; a flexible diaphragm partially defining an auxiliary fluid chamber filled with the non-compressible fluid and whose volume is variable; a first partition wall fixed to the second mounting member and partially defining the primary fluid chamber on one of opposite sides thereof and the auxiliary fluid chamber on the other side thereof; a first orifice passage formed at a central portion of the first partition wall for fluid communication between the primary and auxiliary fluid chamber; and an elastic oscillating plate having an annular or a cylindrical shape and disposed radially outwardly of the orifice passage so as to continuously extend in a circumferential direction thereof, the elastic oscillating plate partially defining the primary fluid chamber on one of opposite sides thereof and an oscillating air chamber on the other side thereof, the oscillating air chamber being applied with a periodic change of an air pressure so as to apply to the elastic oscillating plate an oscillating force whose frequency is corresponding to that of vibrations to be damped, whereby the vibration damping device exhibits an active damping effect with respect to the vibrations to be damped.
In the fluid-filled vibration damping device constructed according to the present mode of the invention, the first orifice passage is formed in the central portion of the first partition wall and the annular or cylindrical elastic oscillating plate is disposed radially outwardly of the first orifice passage, making it possible to increase a diameter of the elastic oscillating plate, without taking into account the provision of the first orifice passage. Since the elastic oscillating plate with the increased diameter has a large circumferential length at its outer circumferential portion, the elastic oscillating plate can provide the sufficiently large area thereof at its outer circumferential portion. Thus, the arrangement of this mode (1) assures a sufficiently large area of the elastic oscillating plate without an increase of an external dimension of the device, thereby permitting a sufficient amount of change in a fluid pressure in the primary fluid chamber. Thus, the fluid-filled vibration damping device can exhibits an active vibration damping effect even to input vibrations having a relatively large amplitudes.
In addition, the use of the elastic oscillating plate having the annular or cylindrical shape, prevents the elastic oscillating plate to have an excessively large free length thereof, i.e., a distance between the fixing portions of the elastic oscillating plate to the other components of the device, thereby restricting the maximum displacement of the oscillating plate upon oscillation thereof caused by the periodic change of the air pressure applied to the oscillating air chamber. That is, the use of the annular or cylindrical elastic oscillating plate is effective to avoid the increase of the external dimension of the device with high efficiency, and to prevent the interference of the elastic oscillating plate with the other elements incorporated within the device.
(2) A fluid-filled vibration damping device according to the above mode (1), wherein the second mounting member includes a cylindrical wall portion one of axially opposite open ends of which is opposed to the first mounting member with a spacing therebetween, the elastic body elastically connects the first mounting member with the one of axially opposite open ends of the cylindrical wall portion of the second mounting member such that the one of axially opposite open ends of the cylindrical wall portion of the second mounting member is fluid-tightly closed by the elastic body, the flexible diaphragm fluid tightly closes the other open end of the cylindrical wall portion of the second mounting member, and the first partition wall is supported by and disposed within the cylindrical wall portion of the second mounting member and cooperates with the flexible diaphragm to define therebetween the auxiliary fluid chamber, the vibration damping device further comprising a central tube member fixedly disposed through the first partition wall so as to extend straightly substantially in a center axis of the first partition wall over the primary and auxiliary fluid chambers, the central tube member having a bore serving as the first orifice passage, the elastic oscillating plate having a generally annular shape and being fixedly supported at an inner peripheral portion thereof by the central tube member onto which the inner peripheral portion of the elastic oscillating plate is press-fitted, and while being fixedly supported at an outer peripheral portion thereof by the cylindrical wall portion of the second mounting member, the elastic oscillating plate and the first partition wall being opposed to each other with a spacing therebetween to define therebetween the oscillating air chamber.
In this mode (2), the cylindrical portion of the second mounting member is effectively utilized to accommodate components of the device. Namely, the components of the device is effectively arranged within the cylindrical portion of the second mounting member, making it possible to form the primary fluid chamber, the oscillating air chamber and the auxiliary fluid chamber with a simple structure. The second mounting member may be constituted by a hollow cylindrical member which is open at its axially opposite end faces, or alternatively by a cup shaped member which is open only in its one axial end which is opposed to the first mounting member. The second mounting member may otherwise have a split structure consisting of a plurality of cylindrical members which are superposed on each other in their axial direction and fixed together at their abutting portions by calking. In this case, the elastic oscillating plate and the partition wall may be fixed to the second mounting member such that the outer peripheral portions of the elastic oscillating plate and the partition wall are griped by and compressed between the abutting portions of the cylindrical members.
Further, the elastic oscillating plate is fixedly supported at its central portion by the central tube member which is disposed substantially coaxially with the first partition wall so as to extend straightly in the center axis of the first partition wall, while being fixedly supported at its outer peripheral portion by the second mounting member. In this arrangement, the inner diameter of the elastic oscillating plate is desirably made smaller, since the central tube member serving as the first orifice passage is a straight tube member, while the outer diameter of the elastic oscillating plate is desirably made larger, since the outer diameter is dimensioned without being limited by the provision of the first orifice passage, making it possible to obtain the effective area of the elastic oscillating plate with further improved efficiency. Since the central portion of the elastic oscillating plate is fixedly supported by the central tube member, the free length of the elastic oscillating plate is effectively restricted, thereby limiting the maximum amount or amplitude of elastic deformation of the elastic oscillating plate, minimizing a required space for accommodating the elastic oscillating plate and reducing an overall size of the vibration damping device. Further, the minimized amount of displacement of the elastic oscillating plate permits an improved oscillation responsibility of the elastic oscillation plate upon oscillation of the elastic oscillation plate at medium- and high-frequency bands, resulting in improved active damping effect of the vibration damping device with respect to medium and high frequency vibrations.
The first and second mounting members may preferably be formed of rigid materials such as metal. For effective damping of input vibrations based on resonance of the non-compressible fluid flowing through the first orifice passage, it is preferable to use the non-compressible fluid whose viscosity is not higher than 0.1 Pa.s. The elastic oscillating plate is required to be impermeable with respect to the non-compressible fluid and to be deformable by the periodic change of the air pressure in the oscillating air chamber. Preferably, a rubber elastic layer may be used as the elastic oscillating layer. Alternatively, a synthetic resin layer, a metallic leaf spring, or the like may also be employed as the elastic oscillating plate. The periodic change of the air pressure in the oscillating air chamber may be caused between two different negative values, between two different positive values or between negative and positive values, or alternatively between the atmospheric pressure and a predetermined negative or positive value. Where the present vibration-damping device is used for a motor vehicle having an internal combustion engine, the negative pressure for the damping device is readily available from the engine. Accordingly, the oscillating air chamber is alternately connected to the negative source of the engine and the atmosphere via a valve, whereby the periodic change of the air pressure in the oscillating air chamber may be caused, for example. The central tube member serving as the first orifice passage is preferably formed of a rigid material so as to keep the shape of the orifice passage constant. A cylindrical member made of metal or a synthetic resin material is desirably employed as the tube member, in the light of its efficiency in manufacture. The method or structure for fluid-tightly fixing the inner and outer peripheral portions of the elastic oscillating plate to the sides of the cylindrical tube member and the second mounting member, is not particularly limited, but may be selected from bonding, clamping or press fitting, for example. Preferably, the outer circumferential surface of the elastic oscillating plate is fluid-tightly fixed to the cylindrical portion of the second mounting member by calking.
(3) A fluid-filled vibration damping device according to the above mode (2), wherein the elastic oscillating plate has a tapered cylindrical shape and disposed radially outwardly of the central tube member so that the elastic oscillating plate cooperate with the first partition wall to define therebetween an annular void disposed radially outwardly of the central tube member and extending in a circumferential direction thereof while being open in a circumferential surface thereof, the opening of the annular void being fluid-tightly closed by the cylindrical wall portion of the second mounting member, to thereby define the oscillating air chamber interposed between the elastic oscillating plate and the first partition wall.
In this mode (3), the elastic oscillating plate is arranged to have the tapered cylindrical shape, permitting to effectively provide a relatively large area of the elastic oscillating plate, without an increase of the outer diameter of the elastic oscillating plate, in comparison with the case where a plane annular elastic oscillating plate is used. Meanwhile, an air inlet port for introducing a pressured air into the oscillating air chamber may be formed through the cylindrical wall portion of the second mounting member.
(4) A fluid-filled vibration damping device according to claim 1, wherein the second mounting member includes a cylindrical wall portion one of axially opposite open ends of which is opposed to the first mounting member with a spacing therebetween, the elastic body elastically connects the first mounting member with the one of axially opposite open ends of the cylindrical wall portion of the second mounting member such that the one of axially opposite open ends of the cylindrical wall portion of the second mounting member is fluid-tightly closed by the elastic body, the flexible diaphragm fluid tightly closed the other open end of the cylindrical wall portion of the second mounting member, and the first partition wall is supported by and disposed within the cylindrical wall portion of the second mounting member, the first partition wall partially defining the primary fluid chamber on one of opposite side thereof and the auxiliary fluid chamber on the other side thereof, the elastic oscillating plate having a generally cylindrical shape and disposed within the primary fluid chamber such that axially opposite end portions of the elastic oscillating plate are supported by respective axial portions of the cylindrical wall portion of the second mounting member, the elastic oscillating plate partially defining the primary fluid chamber on an inner circumferential side thereof and cooperating with the cylindrical wall portion of the second mounting member to define therebetween the oscillating air chamber on an outer circumferential side thereof.
In this mode (4), the elastic oscillating plate has a cylindrical shape and is disposed in the outer circumferential portion of the vibration-damping device. Therefore, the elastic oscillating plate may be formed with a relatively large circumferential length, permitting an increase of the area of the elastic oscillating plate, while avoiding undesirable increase of the external dimensions of the vibration-damping device. The use of the cylindrical elastic oscillating plate makes it possible to obtain a sufficiently large area of the elastic oscillating plate and to provide a relatively large space in a radially inward portion of the elastic oscillating plate. The large space in the elastic oscillating plate permits to provide the first orifice passage with a relatively large cross sectional area or a relatively large length, leading to a high degree of freedom in tuning the first orifice passage, and a resultant high degree of freedom in tuning the damping characteristics of the vibration damping device.
(5) A fluid-filled vibration damping device according to the above mode (4), wherein the first orifice passage extends annularly or helically in the circumferential direction of the first partition wall. In this mode (5) the length of the first orifice passage is made larger, leading to an increase in an amount of flow of the fluid through the first orifice passage, whereby the vibration damping device can exhibit an improved damping effect based on flows of the fluid through the first orifice passage. In particular, the combination use of the annularly or helically extending first orifice passage and the cylindrical elastic oscillating plate makes it possible to provide a space large enough to form the first orifice passage in the radially inner portion of the elastic oscillating plate, without increasing the external dimension of the vibration damping device, and without limiting the size of the area of the elastic oscillating plate. Thus, the first orifice passage can be formed with the relatively large length.
(6) A fluid-filled vibration damping device according to any one of the above-indicated modes (1)-(5), the further comprising a second partition wall fixed to and supported by the second mounting member, such that the second partition member divides the primary fluid chamber into a pressure receiving chamber partially defined by the elastic body and filled with the non-compressible fluid a pressure of which changes due to an elastic deformation of the elastic body, and an oscillating fluid chamber partially defined by the elastic oscillating plate and filled with the non-compressible fluid a pressure of which changes due to displacement of the elastic oscillating plate, and a second orifice passage for fluid communication between the pressure receiving chamber and the oscillating fluid chamber.
In the vibration-damping device constructed according to the mode (6) of the invention, the pressure change of the fluid filling the oscillating fluid chamber is induced by the displacement of the elastic oscillating plate, and is transmitted to the pressure receiving chamber via the second orifice passage. Based on resonance of the fluid flowing through the second orifice passage, the pressure change of the fluid in the oscillating fluid chamber is effectively transmitted to the pressure receiving chamber with high efficiency, thereby generating a relatively large oscillating force with an improved energy efficiency. The structure or shape of the second orifice passage is not particularly limited, but may be suitably determined, taking into consideration required vibration damping characteristics of the device. For instance, the second orifice passage may be constituted by a single fluid passage continuously extending, or alternatively by a plurality of through hole each extending through the wall thickness of the second partition wall.
(7) A fluid-filled vibration damping device according to the above indicated mode (6), wherein the first and second partition walls are superposed on each other and cooperate to define at central portion thereof the first orifice passage. In this mode (7) of the invention, the first orifice passage is formed by utilizing the first and second partition walls with high efficiency, leading to an increased high degree of freedom in designing the shape and structure of the first orifice passage and in tuning the first orifice passage, and leading to a reduced number of the required components for forming the first orifice passage.
(8) A fluid-filled vibration damping device according to the above-indicated mode (6) or (7), wherein the elastic oscillating plate has an annular plate-like shape and is interposed between outer circumferential portions of the first and second partition walls which are superposed on each other, the elastic oscillating plate cooperating with the first partition plate to define therebetween the oscillating air chamber, while cooperating with the second partition plate to define therebetween the oscillating fluid chamber.
In the vibration-damping device according to this mode (8) of the invention, the first and second partition walls are superposed on each other to define therebetween a spacing which is effectively utilized to form the oscillating fluid and air chambers, resulting in a reduced number of the required components for forming the oscillating fluid and air chambers. Further, the central portions of the first and second partition walls are effectively utilized to form the first orifice passage.
(9) A fluid-filled vibration damping device according to any one of the above-indicated modes (6)-(8), wherein the first orifice passage is formed through the first and second partition wall such that the first orifice passage extends straightly in the center axes of the first and second partition walls, and the second orifice passage is disposed radially outwardly of the first orifice passage so as to extend in a circumferential direction.
According to the vibration damping device of this mode (9) of the invention, the length of the second orifice passage can be made larger, while holding the overall size of the device in compact, leading to a higher degree of freedom in tuning the second orifice passage. The arrangement of this mode (9) facilitates to form the first and second orifice passages independent from each other, such that the first and second orifice passages have respective cross sectional areas or lengths, resulting in high facility in tuning the first and second orifice passages independently of each other.
(10) A fluid-filled vibration damping device according to any one of the above-indicated modes (6)-(8), wherein the second orifice passage is formed in a radially intermediate portion of the second partition wall so as to extend in a circumferential direction of the second partition wall, one of opposite ends of the second orifice passage, which end is connected to the oscillating fluid chamber, further extends so as to be connected with the auxiliary fluid chamber, so that the first orifice passage is formed by partially utilizing the second orifice passage.
In the vibration-damping device of the mode (10) of the invention, the first and second orifice passages are connected in series with each other, making it possible to reduce a space required for forming the first and second orifice passages, in comparison with the case where the first and second orifice passage are formed independently of each other. Further, the first orifice passage is partially defined by utilizing the second orifice passage, assuring a sufficiently large length of the first orifice passage with high efficiency.
(11) A fluid-filled vibration damping device according to any one of the above-indicated modes (1)-(10), wherein the vibration damping device elastically connects the two members of the vibration system, or elastically mount one of the two members on the other members such that the first mounting member is fixed to one of the two members in the vibration system, while the second mounting member is fixed to the other member in the vibration system.
According to this mode (11) of the invention, the vibration-damping device is suitably utilized as a vibration damping mount or suspension busing for automotive vehicles, such as an engine mount, a body mount, and a cab mount.
(12) A fluid-filled vibration damping device according to any one of the above-indicated modes (1)-(11), wherein one of the first and second mounting members is fixed to a vibrative member whose vibration to be damped, and the other of the first and second mounting members is connected to the vibrative member via the elastic body, the other of the first and second mounting members cooperating with the elastic body to constitute a secondary vibration system.
According to this mode (12) of the invention, the vibration-damping device is suitably utilized as a dynamic damper or a vibration damper (or oscillator) fixed to a specific portion such as a floor of an automotive vehicle, for example.